The effects of dietary supplements of arginine (30 g/d for 3 d) on protein synthesis and cell proliferation in malignant tumors and normal tissues are being investigated in cancer patients and healthy volunteers. Preliminary studies have suggested that the two-fold stimulation of protein synthesis and Ki67 expression by arginine previously observed in breast tumors might not occur in other tumors or healthy tissues. Arginine supplements are therefore being given to cancer patients for 3d prior to surgery, and tissue and tumor samples are being collected during the operation. Similar patients without dietary supplements serve as controls. Patients with cancer of the prostate, breast, colon and bladder are currently being investigated. Future studies will also include lung cancer, as well as protein synthesis in blood lymphocytes of healthy volunteers.